1. Field of the Invention
The present invention relates to a pipe for an automobile, the pipe having a heat-resistant and corrosion-resistant plated layer that is excellent in workability. More specifically, the invention relates to a pipe that includes a ZnNi-alloy plated layer as a heat-resistant and corrosion-resistant plated layer on an outer surface of a base steel pipe and that has excellent workability.
2. Description of the Related Art
Conventionally, a product, in which a Zn plated layer is formed on a surface of a steel pipe and a chromate film is then formed thereon, has been widely used, for example, as a fuel pipe of an automobile. However, when such a product after a plated-layer treatment is subject to a bending process, corrosion resistance of a bent portion is significantly damaged, and thus heat resistance is also insufficient. In addition, a temperature inside an engine room has increased due to a reduction in an engine size (miniaturization) of an automobile in consideration of low fuel consumption and environmental countermeasure, and accordingly, a demand for higher heat resistance and corrosion resistance has also increased with respect to a pipe to be used inside the engine room.
With regard to heat-resistance and corrosion-resistant plating excellent in workability, the following steel materials have been suggested: a heat-resistant and corrosion-resistant multi-layered plating steel material in which a Ni plated layer is formed as a first layer on a surface of a base material, and a chromate treatment is then performed on a surface of a ZnNi alloy plated layer that is deposited on the Ni plated layer (refer to Japanese Patent Application Laid-Open No. 02-120034 A and Japanese Patent Application Laid-Open No. 10-121267); and a steel material in which a Ni plated layer is formed as a first layer, a ZnNi alloy plated layer is formed thereon as an intermediate layer using an acidic bath, and a ZnNi alloy plated layer is formed thereon as a third layer using an alkaline bath (refer to Japanese Patent Application Laid-Open No. 08-134685).
However, in a production process of a pipe for an automobile, such as a fuel pipe, it is preferable to bend a product after performing plating and chromate treatments on a long straight steel pipe from the viewpoints of productivity, cost, and the like. Accordingly, in the case of independently forming the ZnNi alloy plated layer on the Ni plated layer as described in the conventional art, there is a problem in that the plated film thickness on an end of a pipe becomes large and thereby the workability tends to deteriorate, or adhesiveness between the Ni plated layer and the ZnNi alloy plated layer decreases during bending process and thereby heat resistance and corrosion resistance tend to decrease. In addition, even in the case of forming a plurality of the ZnNi alloy plated layers on the Ni plated layer, there is a problem in that complicated bath management and an increase in cost may be caused.
The present invention has been made to solve the problems in the conventional art, that is, a problem of workability deterioration in the case of a pipe including a ZnNi alloy plated layer independently formed on a Ni plated layer, a problem of a decrease in heat resistance and corrosion resistance due to a decrease in adhesiveness between the Ni plated layer and the ZnNi alloy plated layer during a bending process, and a problem of an increase in the cost in the case of the formation of a plurality of the ZnNi alloy plated layers on the Ni plated layer. Accordingly, an object of the invention is to provide a pipe that includes a heat-resistant and corrosion-resistant plated layer, does not required a Ni plated layer as a first layer, requires low cost, and has excellent workability and high quality.